Method and apparatus for time-warping a digitized waveform to have an approximately fixed period

• US 6,590,946 B1
• Filed: 01/25/2000
• Issued: 07/08/2003
• Est. Priority Date: 01/27/1999
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Chong, Nicola Raewyn, Burnett, Ian Shaw
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US09/490,607
• Time in Patent Office: 1,260 Days
• Field of Search: 375/340, 375/254, 375/242, 375/240, 704/200, 704/214, 704/219, 704/220
• US Class Current: 375/340
• CPC Class Codes: G10L 21/04 Time compression or expansion
• CPC Class Codes: H04B 1/66 for reducing bandwidth of signals; for improving efficiency of transmission H04B1/68 takes precedence

Abstract

An input sequence of unwarped signal samples is stored in an input buffer (101). A pitch and voicing analysis unit (103), which analyzes voicing classification data from the input buffer (101), provides a voicing classification variable indicating whether the voicing classification data is voiced or unvoiced and a preliminary estimate of the signal period in the interval spanned by the voicing classification data to a pitch pulse detection unit (104). The pitch pulse detection unit (104), also using analysis frame data from the input buffer (101), provides a set of locations of unwarped pitch pulses contained in the interval spanned by the analysis frame data to a mapping optimization unit (105). The mapping optimization unit (105) provides a set of parameters describing a mapping from an unwarped time-scale to a warped time-scale, to a warped sampling instant calculation unit (106). The warped sampling instant calculation unit (106) provides a set of warped sampling instants to a warped sample value calculation unit (107). The analysis frame data is also conveyed from the input buffer (101) to the warped sample value calculation unit (107), which provides a set of warped signal samples to an output buffer (108).

Claims

1. A method of generating a set of warped signal samples, the method comprising the steps of:

receiving a sequence of unwarped signal samples, wherein the unwarped signal samples represent the amplitudes of a continuous input signal measured at unwarped sampling instants, wherein the unwarped sampling instants are discrete points on a continuous unwarped time-scale, and wherein the sequence includes at least as many unwarped signal samples as exist in an interval of time equal to the expected maximum value of signal period, wherein signal period is a slowly varying function of time such that the amplitude of a signal at a first point in time is approximately equal to the amplitude at a second point displaced from the first point by an interval equal to the signal period at the first point;

storing the received sequence in a buffer;

determining unwarped pitch pulse locations within an interval spanned by a particular analysis frame, wherein pitch pulses are strong peaks occurring once per period in the input signal, unwarped pitch pulse locations are points on the unwarped time-scale at which pitch pulses occur, and an analysis frame is a predetermined segment of samples in the buffer;

determining an invertible mapping that associates all points within an interval on the continuous unwarped time-scale spanned by the analysis frame with corresponding points on a continuous warped time-scale, such that the mapping can be completely described by a finite number of parameters, and such that if pitch pulses occur within the interval, the mapping minimizes a measure of deviation between warped pitch pulse locations and a predetermined set of desired warped pitch pulse locations, wherein warped pitch pulse locations are points on the warped scale with which the mapping associates the unwarped pitch pulse locations;

determining warped sampling instants, wherein warped sampling instants are points on the original time-scale that are within the time interval spanned by the analysis frame, and which correspond to predefined points on the warped scale; and

interpolating between the unwarped signal samples to compute a set of warped signal samples, wherein the warped signal samples are the values of the continuous input signal at the warped sampling instants.

2. A method of generating a set of warped signal samples according to claim 1, wherein the mapping between the unwarped and warped time-scales is such that points on the unwarped scale separated by one period are associated with points on the warped scale that are separated approximately by a warped period, wherein the warped period is a predetermined fixed interval.

3. A method of generating a set of warped signal samples according to claim 2, wherein the desired warped pitch pulse locations are points on the warped time-scale that are separated by exactly one warped period.

4. A method of generating a set of warped signal samples according to claim 1, wherein some quantity of previously received unwarped signal samples are also stored in the buffer.

5. An apparatus for generating a set of warped signal samples, the apparatus comprising:

an input terminal for receiving a sequence of unwarped signal samples, wherein the unwarped signal samples represent the amplitudes of a continuous input signal measured at unwarped sampling instants, wherein the unwarped sampling instants are discrete points on a continuous unwarped time-scale, and wherein the sequence includes as many unwarped signal samples as exist in an interval of time equal to the expected maximum value of signal period, wherein signal period is a slowly varying function of time such that the amplitude of a signal at a first point in time is approximately equal to the amplitude at a second point displaced from the first point by an interval equal to the signal period at the first point;

a buffer having an input coupled to the input terminal for storing the received sequence of unwarped signal samples;

a first analyzer coupled to the buffer to analyze the data within the buffer and to determine unwarped pitch pulse locations within an interval spanned by an analysis frame, wherein pitch pulses are strong peaks occurring once per period in the input signal, unwarped pitch pulse locations are points on the unwarped time-scale at which pitch pulses occur, and an analysis frame is a predetermined segment of samples in the buffer;

a second analyzer coupled to the first analyzer to analyze the unwarped pitch pulse locations and to determine an invertible mapping that associates all points within an interval on the continuous unwarped time-scale spanned by the analysis frame with corresponding points on a continuous warped time-scale, such that the mapping can be completely described by a finite number of parameters, and such that if pitch pulses occur within the interval, the mapping minimizes a measure of deviation between warped pitch pulse locations and a predetermined set of desired warped pitch pulse locations, wherein warped pitch pulse locations are points on the warped scale with which the mapping associates the unwarped pitch pulse locations;

a third analyzer coupled to the second analyzer to analyze the parameters of the mapping and to determine warped sampling instants, wherein warped sampling instants are points on the original time-scale that are within the time interval spanned by the analysis frame, and which correspond to predetermined points on the warped time-scale; and

an interpolator coupled to the third analyzer for interpolating between the unwarped signal samples to compute a set of warped signal samples, wherein the warped signal samples are the values of the continuous input signal at the warped sampling instants.

6. An apparatus for generating a set of warped signal samples according to claim 5, wherein the first analyzer comprises a pitch and voicing analysis unit having a first input coupled to a first output of the input buffer for receiving voicing classification data, and a pitch pulse detection unit having an input coupled to a second output of the input buffer for receiving frame data, the pitch and voicing analysis unit providing preliminary period information and voicing classification information to the pitch pulse detection unit.

7. An apparatus for generating a set of warped signal samples according to claim 6, wherein the second analyzer comprises a mapping optimization unit having a first input coupled to the pitch and voicing analysis unit for receiving the voicing classification information and a second input coupled to the pitch pulse detection unit for receiving pulse location information.

8. An apparatus for generating a set of warped signal samples according to claim 7, wherein the third analyzer comprises a warped sampling instant calculation unit having an input coupled to the mapping optimization unit for receiving the set of mapping parameters and determining the warped sampling instants therefrom.

9. An apparatus for generating a set of warped signal samples according to claim 8, wherein the interpolator comprises a warped sample value calculation unit having a first input coupled to the warped sampling instant calculation unit and a second input coupled to the input buffer for receiving the frame data, the warped sample value calculation unit calculating values of the warped signal samples.